Mayer Brown partner Elizabeth Espín Stern is based in Washington, D.C., not London or Brussels. But Brexit has been her business ever since Britons signed on to the idea of ditching the European Union in 2016.

The United Kingdom is set to formally withdraw by the end of the month—three and a half years after the Brexit referendum, and six years after Stern launched Mayer Brown’s global mobility and migration practice in 2014.